Fuel consumption = 8 L/100 km
Distance = 350 km
Fuel used = (8/100) * 350 = 28 L

Let x = original acid volume
0.3*(x + 20) = x , 0.3x + 6 = x 0.7x = 6 x = 8.57 L
Add 10 L acid , Total acid = 8.57 + 10 = 18.57 L
Total solution = 18.57 + 20 = 38.57 L
New % = (18.57 / 38.57)*100 = 48.14%

a = (v - u)/t
a = (20 - 0)/10
a = 20/10 = 2 m/s^2

Initial price = 50
After 8% rise = 50 * 1.08 = 54
After 5% fall = 54 * 0.95 = 51.3
Final price = $51.3

Distance = 150 km, Speed1 = 40, Speed2 = 50
Relative speed = 40 + 50 = 90 km/h
Time = Distance / Relative speed = 150 / 90 = 1.667 h = 1 h 40 min

Time = 150 km / 90 km/h = 1.666... hours.

To express this in hours and minutes, 1.666... hours is 1 hour and (0.666... * 60) minutes, which is approximately 1 hour and 40 minutes.
Therefore, the trains will meet in approximately 1 hour and 40 minutes.